Memory array



y 14, 1963 J. 5. EGGENBERGER 3,089,222

MEMORY ARRAY Original Filed Nov. 25, 1958 2 Sheets-Sheet 1 FIGJ SATURATION MAGNETISM, Bm,

(KILOGAUSS) PERCENT BY WEIGHT cu EMBODI MENT No.1

MOLTEN PERFORATED COPPER STRIP FIG.5

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May 14, 1963 J. 5. EGGENBERGER 3,089,222

MEMORY ARRAY Original Filed Nov. 25, 1958 2 Sheets-Sheet 2 EMBODIMENT NO.2

FIG.6 FIG.8

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EMODIMENT No.3

{WP i F1 1" i L. L4 LJ l I r'-1 r #1 l r-n u u u R u U @E @w I I Ffi 1 M M w J I I COPPER ELECTRO-PLATED \FUSED COPPER PLATING AND COPPER MASKS APERTURED METAL APERTURED METAL STRIP STRIP (WITH MASKS REMOVED) United States Patent This application is a division of Serial No. 776,259, filed November 25, 1958.

This invention relates to a metallic memory array and more particularly to a means for fabricating such an array wherein isolation of the individual memory areas is provided.

As it is well known in the art, metallic films either evaporated, electrodeposited, or rolled into a form of thin films or sheets, may be used as memory storage elements in computer mechanisms. While the feasibility of using such memory elements has been demonstrated for single memory bits, only a few memory arrays have thus far been provided. One scheme \for preparing such an array is described in detail in a co-pending application entitled, Electrode and Probe Sensing Method, filed by Robert Ward, Serial No. 748,919 and assigned to the same assignee as this invention. This scheme describes a method for sensing a change in state of a magnetic material during switching and uses rolled sheets of a ferromagnetic metal such as permalloy as memory material. It is desired to improve this array by providing better isolation for each memory bit.

Still another process for producing a memory array comprises punching holes in a sheet of thin magnetic material in order to allow individual wires to be run through the memory areas. Multipath logical arrays such as those described in the copending application Serial No. 706,179 filed December 17, 1957 by L. A. Russell and assigned to the same assignee as this invention, are generally fabricated by running wires from one logical element to another, utilizing air to isolate each magnetic element.

Accordingly, an object of this invention is to provide new and improved computer devices.

A further object is to provide methods whereby memory storage devices may be fabricated wherein the individual memory bits are magnetically isolated one from the other.

Still another object is to provide a logical array in which each logical element is magnetically insulated from other elements in the array.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of example, the principle of the invention and the best mode, which has been contemplated of applying that principle.

In the drawings:

FIGURE 1 shows the relationship of room temperature saturation magnetization, Bm, versus percentage by weight copper added to the alloy system 80-20% by weight nickel-iron.

FIGURES 2-5 illustrates the steps of a process of preparing a memory array according to one embodiment of the present invention.

FIGURE 2 is a schematic representation of an apertured copper sheet having a sectional view as shown in FIGURE 2a.

FIGURE 3 shows a thin sheet of magnetic material having a sectional view as shown in FIGURE 3a.

FIGURE 4 shows the apertured copper sheet positioned on the magnetic sheet prior to sintering.

tion to -20 nickel-iron. A second effect of 3,089,222 Patented May 14, 1963 "ice FIGURE 5 shows the completed memory array prepared by sintering the assemblege of FIGURE 4 and has a sectional view as shown in FIGURE 5a.

FIGURES 6-8 show another embodiment by which an improved memory array may be prepared.

FIGURE 6 shows an apertured metallic sheet having a sectional view as shown in FIGURE 6a.

FIGURE 7 shows an apertured copper sheet, as shown in FIGURE 1, positioned on the apertured metallic sheet prior to sintering.

FIGURE 8 shows the completed memory array prepared by sintering the assemblage of FIGURE 7 which has a sectional view as shown in FIGURE 8a.

FIGURES 9 and 10 describe a process for preparing an improved array of logical elements.

FIGURE 9 shows a schematic representation of an apertured metallic sheet provided with a layer of copper deposited over a plurality of masks having a sectional view as shown in FIGURE 9a.

FIGURE 10 is a representation of a plurality of logical elements after *sintering the structure shown in FIGURE 9 and having a sectional view as shown in FIGURE 10a.

The techniques of the present invention provide means adaptable to large scale automatic processing whereby computer arrays may be fabricated with more desirable magnetic properties than have hitherto been obtainable. Particularly advantageous is the processing of metallic memory and logical arrays from thin sheets of magnetic material. The process described herein are based upon the observed magnetic characteristic of the nickel-ironcopper system. As is shown in FIGURE 1 the saturation magnetization of alloys in the Fe-Ni-Cu system is sharply dependent upon the percentage of copper addithe copper addition is due to precipitation of a second phase at high copper concentrations. For additions to an 80-20 nickel-iron alloy the solubility limit of copper is about 37 weight percent at room temperature. The precipitation of this second phase also results in a sharp increase in coercive force. Furthermore, additions of copper in the order of 50% or more cause a severe reduction in magnetization and increase in coercive force, making the material, in effect, non-ferromagnetic. This effect is most pronounced in the range 37-60% Cu. The properties obtainable in this range in the three component system are utilized to prepare the improved computer arrays shown herein.

In essence, therefore, the present invention achieves isolation of magnetic areas by providing substantially nonmagnetic regions between memory areas. One particular embodiment illustrates the efiect in a thin magnetic film memory array. Another utilizes it in a logical array. Furthermore, methods are indicated wherein these arrays maybe fabricated.

According to one embodiment, as shown most particularly in FIGS. 2-5, an apertured copper sheet, shown in FIGURES 2 and 2a, is provided and placed over a rolled or otherwise prepared thin magnetic sheet such as a permalloy sheet, shown in FIGURES 3 and 3a and assembled as shown in FIGURE 4. An alternate manner of making the structure shown in FIGURE 4 is by electroplating over a suitable mask to produce the composite layers. The composite layers are then heated at elevated temperatures to permit the copper to'difiuse into the nickel-iron alloy to form an essentially non-magnetic insulator surrounding each memory bit, as depicted in FIGURES 5 and 5a.

Another embodiment is shown in FIGURES 6-8. An apertured copper sheet is plated or otherwise positioned onto a perforated nickel-iron sheet to form the structure shown in FIGURE 7. The composite layers are then 3 heated to cause diffusion of the copper and the formation, as shown in FIGURE 8, of an apertured thin film memory array in which the memory bit areas are magnetically iso lated from each other by an essentially non-magnetic region comprising the three component alloy system.

The process of the present invention may be utilized as shown particularly in FIGURES 9-10 to provide an array of logical elements which are magnetically insulated from each other. An apertured permalloy plate is provided with an appropriate mask and copper electroplated thereon. The layers are heated to cause diffusion of the copper into the magnetic material so as to provide thereby logical elements separated by a non-magnetic region.

The conditions for carrying out the diffusion step Will vary depending upon the thickness of the metallic sheet. In order that diffusion of copper into the iron-nickel alloy result in an essentially non-magnetic region, it is necessary to heat the materials at for example 1000 C. for a time interval approximately defined by the equation Where T is the annealing time interval in seconds and h is the thickness of the magnetic sheet in cm. For a 0.25 mil permalloy sheet, an annealing time of 90 minutes is suggested using a copper layer of about the same thickness. Under such conditions isolation of memory areas is achieved without noticeable spreading of magnetic material into non-magnetic regions. For example, if round memory bits of a diameter of about 10 mils are separated from each other by a distance of about 10 mils, a spread of the bit diameter of less than 1 mil occurs when copper is diffused into the areas between each bit. This given example above, including other examples are shown below in the form of a table wherein the thickness of the metals is given in mils, and the time T in minutes.

Example 1 2 3 4 As may be seen, decreasing the temperature increases the time as one might expect, while decreasing the thickness of the permalloy sheet to 0.125 mils with a copper sheet of 0.25 mils at 1000 C. yields a faster annealing time. This latter example is then in accordance with the given formula for annealing time T. The examples given above illustrate preferred systems. The practical limits of temperature for annealing is from 500 C.1100 C. The lower limit being dictated by the allowable time for annealing, and the upper limit by thermal properties of the conductor. The range of annealing time is from two to four days at the lower temperature to about 30 minutes at the upper temperature for a magnetic metallic sheet limited to a maximum thickness of approximately 0.25 mil. This maximum thickness is imposed by the damping effect due to eddy currents in the finished product.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A method of making a magnetic memory array Which comprises providing a first sheet of 0.25 mil maximum thickness ferromagnetic material of nickel-iron alloy composition capable of assuming first and second states of flux remanence, and a second sheet of copper having a plurality of spaced apart apertures, assembling said first and second sheet to form a layered structure and heating said structure at an elevated temperature of approximately 1000 C. in an inert atmosphere for a time sufiicient to diffuse said second sheet into said first sheet to form thereby regions of substantially non-magnetic material surrounding the magnetic material.

2. A method of making a magnetic memory array which comprises providing a first sheet of ferromagnetic material of nickel-iron alloy composition, said sheet of ferromagnetic material having a maximum thickness of 0.25 mil and having a plurality of spaced apart apertures, said ferromagnetic material exhibiting a hysteresis characteristic with appreciable remanence, and a second sheet of 'copper having a plurality of spaced apart apertures in concentric relation to the apertures of said first sheet and of a larger diameter, assembling said first and second sheets to form a layered structure and heating said structure at an elevated temperature of about 1000 C. in an inert atmosphere for a time sufficient to diffuse said second sheet into said first sheet to form thereby regions of a nickel-iron-copper alloy composition exhibiting a substantially non-magnetic characteristic surrounding said regions of magnetic material.

3. A method of making a magnetic memory array Which comprises providing a first sheet of ferromagnetic material of nickel-iron alloy composition and having a maximum of 0.25 mil, said ferromagnetic material being capable of assuming first and second states of remanent flux, depositing a layer of copper over a suitable mask having a plurality of spaced apart apertures onto said sheet, heating said layered structure at a temperature of approximately 1000 C. for a time sufiicient to diffuse said copper into said ferromagnetic material to form, thereby, regions of substantially non-magnetic material surrounding the magnetic material.

4. A method of making a memory array which comprises providing a first sheet of nickel-iron alloy ferromagnetic material having a maximum thickness of 0.25 mil and exhibiting appreciable remanence, providing a second sheet of copper which is of 0.25 mil maximum thickness having a plurality of spaced apertures therein, assembling said first and second sheet to form a layered structure and heating said structure to a temperature of approximately 1000 C. in an inert atmosphere for a time given by an expression T=1.5 10 h Where T is given in seconds and h is the thickness of the magnetic sheet in centimeters, whereby said second sheet is diffused into said first sheet to form regions of substantially non-magnetic material surrounding the magnetic material.

References Cited in the file of this patent UNITED STATES PATENTS 1,017,031 Wingaard Feb. 13, 1912 2,633,633 Bogart et a1. Apr. 7, 1953 2,824,294 Saltz Feb. 18, 1958 2,906,682 Fahnoe et a1. Sept. 29, 1959 2,936,435 Buck May 10, 1960 OTHER REFERENCES Technical Bulletin T-34, Brazing and Soldering Nickel and High-Nickel Alloys (pp. 11-13 relied on). Development and Research Division, The International Nickel Co., Inc, 67 Wall Street, New York 5, N.Y., June 1952. 

1. A METHOD OF MAKING A MAGNETIC MEMORY ARRAY WHICH COMPRISES PROVIDING A FIRST SHEET OF 0.25 MIL MAXIMUM THICKNESS FERROMAGNETIC MATERIAL OF NICKEL-IRON ALLOY COMPOSITION CAPABLE OF ASSUMING FIRST AND SECOND STATES OF FLUX REMANENCE, AND A SECOND SHEET OF COPPER HAVING A PLURALITY OF SPACED APART APERTURES, ASSEMBLING SAID FIRST 